This invention relates generally to a nozzle capping device for use in an ink jet printer, and more particularly concerns a device to cap nozzles in an ink jet printhead, when the ink jet printer is not in operation, without the need of moving the printhead or the paper transport.
An ink jet printer may be either the "continuous stream" or the "drop-on-demand" type. In the continuous stream type of printer, ink is emitted under pressure continuously from one or more orifices in a printhead. The ink in the printhead is perturbated by, for example, a piezoelectric device causing the streams of ink to breakup into droplets a predetermined distance from the nozzles where charging electrodes are located. The charging electrodes induce charges on the droplets which are then deflected by fields produced by deflection electrodes as necessary, so that they are deposited either in a specific location on a recording member or, if not required for printing, in a gutter from where they are collected and recirculated. In the drop-on-demand type of printer, ink is contained in a plurality of channels in a printhead under a slightly negative pressure and electrical energy pulses are used to rapidly heat thermal transducers in the channels to form momentary ink vapor bubbles which cause the droplets of ink to be expelled, as required, from orifices at the ends of the channels and to be directed towards a recording member.
When the ink jet printer is not in operation, ink not expelled in one or more orifices can dry and clog the orifice, causing failure or reduced ink flow through the orifice resulting in poor print quality. It is well known that capping of the printhead can prevent ink from drying in the orifices. Thus, ink jet printers have employed a capping station to cap the ink jet nozzles. These capping stations involve moving the printhead to the capping station or moving the paper transport to enable access of a capping device.
In an ink jet printer that has a full width printhead, it has been found that it is undesirable to move the printhead. The alignment of the printhead is difficult to maintain with a printing plane, thus moving the printhead has adverse effect on print quality. Capping of a fixed full width printhead may also be achieved by moving the paper transport out of interference with the path of movement by a capping station, and then placing the capping station into engagement with the printhead, this method may involve a costly and complicated moving mechanism that can fail or wear out. Also, the method of moving the printhead and/or the capping station into engagement with each other or the method of moving the paper transport out of interference with the capping operation may not provide capping protection in the event of a power failure.
Various other approaches have been devised to cap ink jet printhead when the ink jet printer is not in operation, the following disclosure appears to be relevant:
U.S. Pat. No. 4,533,927 to Iwagami et al. discloses a capping mechanism for preventing nozzle blocking in an ink jet system printer. A capping mechanism includes a cap member supported by a slidable plate. The slidable plate is shifted toward the printer head as the printer head moves to the stand-by position through use of links whereby the cap member covers the nozzle portion including the printhead. That is, the slidable plate is shifted by the travel force of the carriage and, therefore, a separate drive source is not required for the slidable plate.
U.S. Pat. No. 4,539,574 to Broome et al. discloses a pen capping mechanism. The system utilizes a flat bar of plastic as a slider member with as upper surface adapted to sealably mate with the tips of the pens. The slider member is supported for longitudinal movement on a support track and is moved between positions by an operator connected thereto.
U.S. Pat. No. 4,543,589 to Terasawa discloses a capping device for ink jet nozzles. The device provides a cap for an ink jet nozzle which prevents an ink pool from forming around the front ends of the nozzle. The capping device includes an ink absorbing element and an elastic member surrounding the ink absorbing element and arranged in a position as to be brought in contact with the ink jet head to tightly seal the front end of the head.
U.S. Pat. No. 4,970,534 to Terasawa et al. discloses an ink jet recovery device having a spring-loaded cap and a mechanism for pressing the cap against a recording head to seal the printhead nozzles. The device comprises an elastic cap that is movable between a retracted position, in which it is spaced from a recording head, and an in-contact position, in which it is pressed against the recording head. The recovery device also includes a rotatable drive gear having a cam surface, with a retracting cam and a compression cam, for moving the cap.
Even with the above-mentioned teaching available, the problem remains with capping the printhead without the need of moving the printhead or the paper transport and capping when a power failure occurs.